Since analogue signals have now disappeared in Melbourne I was looking for a method to send a signal from a set top box to my black and white TV's. I ended up buying a low powered transmitter that I can confirm works really well with a great picture and sound. It is fully programmable so you can select both VHF and UHF frequencies and also change the sound frequency which is good for foreign TV's I recommend this as you can watch programs on multiple sets in the one room without hooking up a modulator which is only good for one TV.

If anyone wants to look at what I got click this link.

http://www.ebay.com.au/itm/HLLY-TVX-50M-0-05W-TV-TRANSMITTER-TV-Exciter-Unique-in-ebay-Black-/261527034532....

Hello Unfortunately it seems to be unavailable now.
Your link just takes me to a list of more modern devices in the same category.
It’s interesting that it was actually called an exciter. Something that most people wouldn’t use as a search term.

I'm sure I've mentioned this one before, but it's worth a re-mention because it's the only totally satisfactory solution that will work with old TVs, especially those with 10 channel tuners.

https://www.gme.net.au/catalogue/modulators/md100vs.aspx

Designed and made in Oz, they are worth the new stock asking price if you want to actually watch your vintage TV!

If you know someone who does antenna installs you may be able to snaffle some of these that have been pulled out of clubs etc in digital upgrades.